A comedian explaining the joke is like Dr. Louis Slotin explaining nuclear fission with a subcritical mass of plutonium, two beryllium reflectors, and a screw driver. It will eventually end their career (becuase Dr. Slotin died of acute radiation syndrome after the screw driver slipped, the beryllium reflectors touched, and the plutonium underwent nuclear fission, delivering a lethal dose of radiation in under a second).